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.TH CURLOPT_HSTSWRITEFUNCTION 3 "14 Sep 2020" "libcurl 7.74.0" "curl_easy_setopt options"
.SH NAME
CURLOPT_HSTSWRITEFUNCTION \- write callback for HSTS hosts
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLSTScode hstswrite(CURL *easy, struct curl_hstsentry *sts,
                      struct curl_index *count, void *userp);

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTSWRITEFUNCTION, hstswrite);
.fi
.SH DESCRIPTION
Pass a pointer to your callback function, as the prototype shows above.

This callback function gets called by libcurl repeatedly to allow the
application to store the in-memory HSTS cache when libcurl is about to discard
it.

Set the \fIuserp\fP argument with the \fICURLOPT_HSTSWRITEDATA(3)\fP option or
it will be NULL.

When the callback is invoked, the \fIsts\fP pointer points to a populated
struct: Read the host name to 'name' (it is 'namelen' bytes long and null
terminated. The 'includeSubDomains' field is non-zero if the entry matches
subdomains. The 'expire' string is a date stamp null-terminated string using
the syntax YYYYMMDD HH:MM:SS.

The callback should return \fICURLSTS_OK\fP if it succeeded and is prepared to
be called again (for another host) or \fICURLSTS_DONE\fP if there's nothing
more to do. It can also return \fICURLSTS_FAIL\fP to signal error.

This option does not enable HSTS, you need to use \fICURLOPT_HSTS_CTRL(3)\fP to
do that.
.SH DEFAULT
NULL - no callback.
.SH PROTOCOLS
This feature is only used for HTTP(S) transfer.
.SH EXAMPLE
.nf
{
  /* set HSTS read callback */
  curl_easy_setopt(curl, CURLOPT_HSTSWRITEFUNCTION, hstswrite);

  /* pass in suitable argument to the callback */
  curl_easy_setopt(curl, CURLOPT_HSTSWRITEDATA, &hstspreload[0]);

  result = curl_easy_perform(curl);
}
.fi
.SH AVAILABILITY
Added in 7.74.0
.SH RETURN VALUE
This will return CURLE_OK.
.SH "SEE ALSO"
.BR CURLOPT_HSTSWRITEDATA "(3), " CURLOPT_HSTSWRITEFUNCTION "(3), "
.BR CURLOPT_HSTS "(3), " CURLOPT_HSTS_CTRL "(3), "
